1. Field of the Invention
This invention relates to flame-retardant compositions and more particularly to stabilized flame-retardant styrenic polymer compositions.
2. Description of the Prior Art
The prior art has taught the use of a variety of flame-retardant agents for use in styrenic compositions such as polystyrene, acrylonitrile-butadiene-styrene ("ABS") copolymers, and the like. Among the flame-retardant agents heretofore employed in such compositions are such bromine-containing agents as tetrabromobisphenol-A, octabromodiphenyl ether, decabromodiphenyl ether, 1,2-bis(2,4,6-tribromophenoxy) ethane, bis(dibromopropyl carbonate) of tetrabromobisphenol-A, and bis(pentabromophenoxy) ethane. The prior art disclosing the use of such bromine-containing compounds as flame retardants in styrenic polymers includes U.S. Pat. No. 3,830,766, U.S. Pat. No. 3,075,944, British patent specification No. 1,372,120, and a variety of others.
Although it has thus been proposed to add various organic bromine compounds to styrenic polymers, compositions so obtained have a tendency to degrade, especially on heating. For example, when such compositions are injection molded, the degradation normally results in severe discoloration of the composition.
It is therefore desirable to include in the composition an antidegradant or stabilizer the function of which is to prevent, or at least seriously retard, deterioration of the polymer arising from decomposition of the organic bromine compound or interaction between the polymer and the organic bromine compound. Thus, the choice of suitable class of stabilizers has been a matter for considerable research even among well-known compounds.
It has heretofore been suggested that dibutyltin maleate and other organo-tin compounds be employed in halogen containing styrenic compositions (e.g., Japanese Pat. No. 72/22090 disclosing the use of 2-15% dibutyltin maleate in polystyrene containing hexabromocyclododecane as the flame-retardant; British patent specification No. 881,578 disclosing stabilized compositions comprising a polymer of a vinyl-aromatic compound, an inorganic ester of a bromo-alkanol as the flame-retardant agent, and an organo-tin compound as the stabilizer; U.S. Pat. No. 3,442,980 describing flame-retardant graft polymer blends of halogen-substituted carboxylic acids and/or acid anhydrides with acrylonitrile-butadiene-styrene graft polymer compositions containing dibutyltin maleate; and U.S. Pat. No. 3,907,932, employing hydrocarbon tin maleates and hydrocarbon tin -- bis-maleate half esters).
Similarly, the prior art has individually suggested the use of hindered phenolic antioxidants and carboxylic acid anhydrides (e.g., U.S. Pat. No. 2,661,347 disclosing the stabilization of polyacrylonitrile with maleic acid and maleic anhydride; and U.S. Pat. No. 3,793,401 describing the use of up to 20% by weight of organic anhydrides in non-flame-retarded polymer compositions containing at least 50 mole-percent of polymerized unsaturated nitriles, such as acrylonitrile and methacrylonitrile, and at least 5% by weight of a diene rubber).
Use of the foregoing stabilizers in accordance with the prior art has not permitted the desired degree of thermal stability to be achieved with styrenic polymer compositions. Moreover, many of the agents suggested in the prior art have been found to be unsuited for such use in accordance with the present invention. The prior art has not suggested the unique combination of agents employed in accordance herewith, much less that synergistic results are achieved when such agents are combined as taught herein.
Accordingly, a primary object of the present invention is to provide stable, flame-retardant styrenic polymer compositions.
Another object is to provide a new and unique stabilizer composition to be employed in bromine-containing flame retardant agents specially suited for use in styrenic polymer compositions.
Yet another object is to provide a stabilizer composition that is especially effective in improving the thermal stability of flame-retardant styrenic compositions incorporating tetrabromobisphenol-A.